In a prior art networked client-server computer system 100 (FIG. 1A), client personal computers (PCs) 101-102 communicate with a file server PC 103 to access shared resources, such as a database file 104 or a printer (not shown). The shared resources are commonly shared by client PCs 101-102 over a network, such as ethernet 105 that interconnects all PCs 101-103.
Data transfer over ethernet 105 between PCs 101-103 is implemented by network adapter cards 131-133 mounted in PCs 101-103 respectively. Network adapter cards 131-133 include: (1) network connectors 141-143 that transmit and receive signals on ethernet 105, (2) filter modules 151-153 that filter noise, and (3) network interface circuits 161-163 that perform the functions of proper addressing, reading and storing of data to be exchanged over ethernet 105. Network interface circuits 161-163 implement a carrier-sense-multiple-access collision-detect (CSMA/CD) protocol during exchange of data.
FIG. 1B illustrates one example of a network adapter card 131, that uses as a network interface circuit 161, for example, AM 79C970 illustrated in FIG. 1C, described in"Ethernet/IEEE 802.3 Family-World Network Data Book/Handbook," 1994 and also described in "PCnet.TM.PCI Hardware Reference Manual" both by AMD, One AMD Place, P.O. Box 3453, Sunnyvale, Calif. 94088-3453, that are both incorporated by reference herein in their entirety. In the example of FIG. 1B, network interface circuit 161 includes a 10BASE-T media attachment unit (MAU) port 162 (FIG. 1C) that implements the 10BASE-T functions defined in Sections 13 and 14 of IEEE Std 802.3i-1990--that is a supplement to ISO/IEC 8802-3:1990, Product Number SH16337, available from IEEE Service Center, 445 Hoes Lane, P.O. Box 1331, Piscataway, N.J., USA 08855-1331 and that is incorporated herein by reference in its entirety. Network interface circuit 161 also includes an attachment unit interface (AUI) port 163 (FIG. 1C) that is implemented as a data terminal equipment (DTE) for attachment to an external MAU (not shown), as an alternative to 10BASE-T MAU port 162.
In a 10BASE-T ethernet, each one of connectors 141-143 (FIG. 1A) of respective network adapter cards 131-133 is connected by Unshielded Twisted Pair (UTP) cables 171-173 to a hub card 180. While a hub card is typically part of a stand-alone hub, for smaller networks (e.g. 8 stations) hub card 180 (FIG. 1A) can be mounted inside file server PC 103 to reduce costs by sharing the PC's chassis, power supply and processor.
FIG. 1D illustrates one example of a prior art hub card 180, that includes as a repeater circuit 199, for example, AM 79C981 illustrated in FIG. 1E, described in "Ethernet/IEEE 802.3 Family-World Network Data Book/Handbook" that was referenced above and also described in"ISA-HUB.TM. User's Manual" that is incorporated by reference herein in its entirety. Repeater circuit 199 has one AUI port and eight 10BASE-T MAU ports. Use of repeater circuit 199 is described in, for example, "IEEE 802.3 Repeater Technical Manual" available from AMD (above) that is also incorporated by reference herein in its entirety. The AUI port of repeater circuit 199 is also implemented as a DTE for attachment to an external MAU (not shown).
Three of the 10BASE-T ports of repeater circuit 199 are coupled through filter modules 191-193 (FIG. 1A) to hub connectors 181-183 that are connected by UTP cables 171-173 to network adapter cards 131-133. Repeater circuit 199 receives packets from any one of attached network adapter cards 131-133 and propagates a received packet to all attached network adapter cards 131-133. During propagation of the received packet, repeater circuit 199 retimes the bits being retransmitted. Repeater circuit 199 also detects collision by monitoring activity on all hub connectors 181-183.
Installation of hub card 180 in file server PC 103 can require an expansion slot that is a scarce and valuable commodity in a file server PC. Therefore it is desirable to support both a repeater circuit and a network interface circuit on a single printed circuit board (PCB).
Network interface circuit 161 and repeater circuit 199 both have AUI ports that can be coupled to each other through a twisted pair ethernet transceiver, e.g. AM 79C98 or AM 79C100 that converts the AUI port signals to 10BASE-T signals, as shown in FIG. 1F, because both AUI ports are implemented as DTEs. Such connections are described in, for example, "IEEE 802.3 Repeater-Technical Manual" referenced above.
However, the use of a twisted pair ethernet transceiver to indirectly couple a network interface circuit and a repeater circuit adds to the cost of the PCB. Moreover, the large number of components results in high power consumption and low reliability that may not be acceptable for some file server applications.